FOSSIL MAMMA.LS. 277 



The second molar, tlie fifth of the dental series, (Figs. 1 and 2, V,) is much larger than the 

 preceding ; has its three principal ridges arranged rather more obliquely to the axis of the 

 tooth ; has a small talon in front, and another much more largely developed behind. The 



dimensions are as follows : 



Indies. 

 Length ----------- 3. 80 



Breadth across first ridge at base ---___ 2. 00 

 Breadth across third ridge at base - - - - - -2.40 



Height of ridges, about -------- I.OO 



The anterior talon, though below the level of the other ridges, is much worn ; it occupies the 

 outer half of the front of the tooth only, and its section gives the half of a trefoil, the folded 

 side being directed backwards. The first ridge is a little worn, and, like the others, is deeply 

 cleft in the centre, the two sides of the cleft being in close contact. The third ridge is fractured ; 

 the inner half being broken away, the cleft is exposed to the depth of three fourths of an inch , 

 The external half of each of the three ridges is folded in such a manner as to form a salient pro- 

 jection or buttress on its anterior and jiosterior face, and each meets a corresponding projection 

 from the ridge in front and behind. The foldings of the inner half of each ridge are not so 

 well defined. The posterior talon is cleft in the middle, and each lateral half is composed of a 

 large, stout tubercle slightly bifid at the apes. There is no basal ridge in this tooth ; but 

 there exists between the first and second and the second and third ridges a lobed projection on 

 the inside, and on the outside, between the first and second ridges, a tubercle.- A thin layer of 

 cement exists in the interstices of the ridges at some points ; and though generally detached or 

 worn off' from the summits, yet in one instance it was found as high as the apex. 



The fragment of a third molar, the sixth of the dental series, (Figs. 1 and 2, VI,) is that of 

 an immature one, still lodged in the socket, the points just reaching to the level of the edge of 

 the alveolus. One ridge, with a small anterior talon, is preserved; also, the broken base of a 

 portion of the second ridge. The anterior one is about one inch and three fourths high, is 

 deeply cleft in the middle, and each half again partially subdivided so as to form two tubercles 

 upon its summit : the external ones are the largest and highest ; the internal tubercles are con- 

 tinuous posteriorly with a salient ridge, that of the outer half of the tooth being the largest. 

 Behind the ridge just described, the tooth becomes suddenly broader, measuring three inches 

 and an eighth in width, the enlargement being made mainly on the outer half. The fangs of 

 the tooth had but just begun to be developed, the crown still consisting of a hollow shell ; no 

 cement was deposited as yet upon the enamel. 



The great increase in size of this tooth anteriorly, when compared with that which precedes it, 

 as well as its actual measurements, indicate that it is the sixth or ultimate member of the entire 

 molar series. By a comparison of the series of lower molar teeth of M. Humboldtii, given by 

 Falconer & Cautley, (PI. 40, Figs. 10, 13, 14, and 15,) wMch comprises the whole series of 

 molars, from the second to the sixth inclusive, it will be seen that while the anterior extremity 

 of each successive tooth up to the fifth is but little broader than that which preceded it, the sixth 

 becomes at once much broader and longer than its predecessor; its greatest breadth being in 

 fronts and gradually diminishing in size to the posterior extremity.* 



*Thj following measurements, from Falconer & Cautley, (PI. xl. Figs. 13, 14, and 15,) will serve to give the proportional 

 sizes of a series of lower teeth, except only of the first : 



Molar II. Fig. 13 2if Inches. 



" III. Fig. 13 3^ " 



" IV. Fig. 15 4^ " 



V. Fig. 15 5fg " 



" VI. Fig. 14 ^ihi " 



The fifth and sixth molars of the jaw from Chile, figured by Blainville, have the following proportions: 

 Molar V. 6 inches. 



"VI. y " 



